In certain pathologies, the spinal canal extending through a patient's vertebrae is or becomes too narrow and constricts the spinal cord extending therethrough. The narrowing may be congenital, potentially affecting patients at any age. Narrowing can also be attributable to other causes, such as age, injury or removal of a spinal disk.
A condition associated with aging, for instance, is spondylolsis, in which intervertebral disc loose water and become less dense. These degenerative changes near the disk can cause an overgrowth of the bone, producing bony spurs called, “osteophytes” that can compress the spinal cord. The constriction of the spinal cord in the cervical spine, for example, often produces pain, weakness, or loss of feeling in extremities. Other causes for narrowing of the spinal canal include disc shrinkage, which causes the disc space to narrow and the annulus to bulge and mushroom out, resulting in pressure on the spinal cord. Degenerative arthritis of facet joints can cause joints to enlarge, or the vertebra to slip with respect to each other, also compressing the spinal cord. Instability between vertebra, such as caused by stretched and thickened ligaments' can also produce pressure on the spinal cord and nerve roots.
Myelopathy, or malfunction of the spinal cord, occurs due to its compression. The rubbing of the spine against the cord can also contribute to this condition, and the spinal cord compression can ultimately compromise the blood vessels feeding the spinal core, further aggravating they myelopathy.
Traditional procedures for decompressing the spinal cord include a laminectomy, in which the lamina and spinal processes are removed to expose the dura covering the spinal cord. Another known procedure is a laminoplasty, in which the lamina is lifted off the dura, but not completely removed. Typically, one side of the lamina is cut, while a partial cut is made on the other side to hinge the lamina away from the spinal cord to increase the size of the spinal canal. A laminoplasty plate is then screwed to a facet and to the hinged open lamina. The plate of an appropriate size is selected and bent to the desired shape and preferably has a plurality of screw holes. A strut of bone can be placed in the open portion within the lamina and the facet to help hold the open position of the lamina. Prior to the operation, the surgeon needs to measure the vertebra to determine the size of the plate necessary for implantation. At that point, a plate can be selected with the appropriate dimensions, and implanted at the site.
A laminoplasty implant is needed that preferably allows its size to be varied prior to implantation, preferably without changing its overall shape or configuration, so that a plate does not have to be custom selected and intensively shaped and formed prior to each surgery.